1. Field of the Invention
This invention relates to a boot type seal, especially adapted for ball and socket type joints, although useful in any installation for sealing relatively articulatable, tiltable or rotatable members while automatically venting or relieving excess pressures such as might be developed by high pressure lubrication or by the accumulation of excessive amounts of lubricants.
2. Related Art
Nearly all original chassis equipment, such as ball joints and tie rod ends, are sealed units. These “lube-for-life” parts are low maintenance since they are sealed, but generally do not have the life of a “greaseable” part. A greaseable part may be greased periodically to replace grease which has escaped or broken down during use, thereby flushing old grease, debris associated with wear of the joint parts or other contaminants (e.g., moisture, dirt or the like) from the joint in the process. Greasable parts offer reduced friction and increase the service life versus a lube-for-life part. Accordingly, greaseable parts are preferred for many applications.
The challenge in designing a dust boot for a greaseable part is that the dust boot must serve as a barrier to prevent contaminants from entering the articulating component. The dust boot must also allow existing grease to escape when the repair technician flushes the part with new grease.
Typical prior art dust boots for these applications utilize a small grease passage and a flexible flap on an outer rim seal to seal the part from contamination while allowing the grease to escape. Often, the annular dynamic wiping lip seals which surround the ball joint stud are interrupted with a bypass flap as well. This bypass flap represents a possible weak spot in the defense against contaminant infiltration, especially given its open relationship alongside the moving surface of the stud. Contaminants which manages to infiltrate the outermost flap can also get drawn through the inner bypass flap as the surface of the stud slides through the wiping lip seals.
The problem, therefore, with prior designs is that sealing capabilities may be compromised in order to ensure that the boot will also be able to allow grease to exit from the dust boot in a controlled manner. Accordingly, there is a need for an improved dust boot design that does not compromise the sealing capability from contaminants while also allowing the dust boot to purge grease during maintenance operations. Furthermore, there is a need for the stud opening of a dust boot to be lubricated as grease exits the dust boot which is not accomplished by prior designs.